Collision detection system and method of estimating target crossing location

This application is a divisional and claims priority from U.S. patent application Ser. No. 10/780,845 filed Feb. 18, 2004 now U.S. Pat. No. 7,369,941.

TECHNICAL FIELD

The present invention generally relates to object collision detection and, more particularly, relates to a collision detection system and method of estimating the crossing location of the object.

BACKGROUND OF THE INVENTION

Automotive vehicles are increasingly being equipped with collision avoidance and warning systems for predicting potential collisions with external objects, such as another vehicle or a pedestrian. Upon detecting a potential collision, such systems are capable of initiating an action to avoid the collision, minimize impact with the object, and/or provide a warning to the vehicle operator. Adaptive cruise control systems have been proposed to track a leading vehicle and automatically control the speed of the following vehicle. The ability to accurately predict an upcoming collision also enables a vehicle controller to control and deploy safety-related devices on the host vehicle. For example, upon predicting an anticipated collision or near collision with an object, the vehicle seat belt pretensioner could be activated in a timely manner to pretension the seat belt, or the air bag system could be readied for quicker activation, thereby enhancing the application of the safety devices. The controller could also deploy a warning signal to notify the vehicle driver of a predicted collision with an object.

In some vehicle target tracking systems, the host vehicle is generally equipped with a sensor arrangement that acquires range, range rate, and azimuth angle (i.e., direction to target) measurements for each tracked target within a field of view. The sensor arrangement employed in such conventional systems generally requires a relatively complex and expensive sensor arrangement employing multiple sensors that are required to measure the azimuth angle of the object, relative to the host vehicle, in addition to obtaining range and range rate measurements of the object. It is generally desirable to reduce the complexity and cost of systems and components employed on automotive vehicles to provide a cost affordable vehicle to consumers.

It has been proposed to reduce the complexity and cost of a vehicle collision detection system by employing a single radar sensor that provides range and range rate measurements of an object and estimates the miss distance of the object. One such approach is disclosed in U.S. Pat. No. 6,615,138, and entitled “COLLISION DETECTION SYSTEM AND METHOD OF ESTIMATING MISS DISTANCE EMPLOYING CURVE FITTING.” The entire disclosure of the aforementioned patent is hereby incorporated herein by reference. Another approach is disclosed in U.S. application Ser. No. 10/158,550, filed on May 30, 2002, and entitled “COLLISION DETECTION SYSTEM AND METHOD OF ESTIMATING MISS DISTANCE.” The entire disclosure of the aforementioned application is hereby incorporated herein by reference. While the aforementioned approaches employing a single radar sensor are well suited to estimate the miss distance of an object, additional information such as the crossing location with respect to the vehicle is generally not available. In some situations, it may be desirable to determine the crossing location of the object with respect to the host vehicle, such as a location on the vehicle front bumper that the object is expected to come into contact with. By knowing the location of the expected collision, countermeasures can be initiated based on the anticipated crossing location.

It is therefore desirable to provide for a vehicle collision detection system that estimates the crossing location of an object. It is further desirable to provide for a reduced complexity and cost affordable vehicle collision detection system that estimates crossing location of an object.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a collision detection system and method of estimating a crossing location of an object are provided. According to one aspect of the present invention, the collision detection system includes a first sensor for sensing an object in a field of view and measuring a first range defined as the distance between the object and the first sensor. The system also includes a second sensor for sensing the object in the field of view and measuring a second range defined by the distance between the object and the second sensor. The system further includes a controller for processing the first and second range measurements and estimating a crossing location of the object as a function of the first and second range measurements.

According to another aspect of the present invention, a method of estimating a crossing location of an object is provided. The method includes the steps of sensing the presence of an object in a field of view, tracking the object with first and second sensors, measuring range to the object with the first sensor, and measuring range to the object with the second sensor. The first and second sensors are separate from each other. The method further includes the step of estimating a crossing location of the object as a function of the range measurement with the first and second sensors.

Accordingly, the collision detection system and method of estimating target crossing location of the present invention advantageously estimates the crossing location of an object without requiring a complex and costly sensor arrangement. By knowing the target crossing location, the present invention advantageously allows for enhanced countermeasures to be employed on a vehicle.

These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

<figref idref="DRAWINGS">FIG. 1</figref> is a plan view illustrating the geometry of a collision detection system employing two sensors on a vehicle according to the present invention;

<figref idref="DRAWINGS">FIG. 2</figref> is a plan view further illustrating the geometry of the detection system shown tracking a target object;

<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram illustrating the collision detection system;

<figref idref="DRAWINGS">FIG. 4</figref> is a block diagram illustrating the target crossing location estimator of the collision detection system;

<figref idref="DRAWINGS">FIG. 5</figref> is a graph illustrating sensed data plotted in a curve in a W-plane;

<figref idref="DRAWINGS">FIG. 6</figref> is a flow diagram illustrating a routine for estimating the crossing location of the target object using the W-plane according to the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 7</figref> is a graph illustrating estimation of the target crossing location according to the first embodiment of the present invention;

<figref idref="DRAWINGS">FIG. 8</figref> is a block diagram illustrating a time-domain approach to estimating the crossing location of a target object according to a second embodiment of the present invention; and

<figref idref="DRAWINGS">FIG. 9</figref> is a flow diagram illustrating a routine for estimating the target crossing location according to the second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to <figref idref="DRAWINGS">FIG. 1</figref>, an automotive vehicle <b>10</b> is generally illustrated having a collision detection system for detecting and tracking an object, and detecting the potential for a collision with the object. The collision detection system includes first and second radar sensors <b>12</b>A and <b>12</b>B mounted to the host vehicle <b>10</b> to cover a desired field of view in front of the vehicle <b>10</b>. The vehicle collision detection system senses and tracks one or more objects, such as a moving target, and estimates a crossing location of the target object relative to a baseline axis of the vehicle <b>10</b>. Using the estimated crossing location of the object, the collision detection system is able to detect an anticipated collision of the target object <b>16</b> with the host vehicle <b>10</b>, thereby allowing for responsive countermeasure action(s) to be taken.

The sensor arrangement includes the first and second sensors <b>12</b>A and <b>12</b>B mounted on opposite sides of the front bumper of vehicle <b>10</b>, according to one embodiment. The first radar sensor <b>12</b>A senses objects in a first field of view <b>14</b>A, and the second sensor <b>12</b>B senses objects in a second field of view <b>14</b>B. The first and second field of views <b>14</b>A and <b>14</b>B substantially overlap to provide a common coverage zone field of view <b>15</b>. Sensors <b>12</b>A and <b>12</b>B sense the presence of one or more objects in field of view <b>15</b>, track relative movement of each of the sensed objects within field of view <b>15</b>, and measure the range (radial distance) to the target object from each sensor. Additionally, sensors <b>12</b>A and <b>12</b>B may further measure the range rate (time rate of change of radial distance) of the target object.

Referring to <figref idref="DRAWINGS">FIG. 2</figref>, the first and second sensors <b>12</b>A and <b>12</b>B are shown separated from each other by a distance d and aligned on a baseline B extending through sensors <b>12</b>A and <b>12</b>B along the y-axis. An x-axis is shown extending through a center point O midway between sensors <b>12</b>A and <b>12</b>B, orthogonal to the y-axis. A target object <b>16</b> is illustrated and is assumed to have a relative velocity vector (relative to the vehicle) parallel to the longitudinal axis (X-axis) of the vehicle <b>10</b> as shown by speed vector S. First sensor <b>12</b>A senses the range R₁defined as the radial distance between first sensor <b>12</b>A and object <b>16</b>. The first sensor <b>12</b>A may also sense the range rate {dot over (R)}₁as the measured rate of change of range R₁of the object <b>16</b> as a function of time relative to the host vehicle <b>10</b>. Second sensor <b>12</b>B measures range R₂defined as the radial distance between second sensor <b>12</b>B and target object <b>16</b>. The second sensor <b>12</b>B may likewise measure the range rate {dot over (R)}₂as the measured rate of change of the range R₂of the object <b>16</b> as a function of time relative to the host vehicle <b>10</b>. Alternately, the range rates {dot over (R)}₁and {dot over (R)}₂may be determined by computing the time rate of change (i.e., derivative) of the corresponding sensed ranges R₁and R₂, respectively.

The first and second sensors <b>12</b>A and <b>12</b>B may each include a commercially available off-the-shelf wide-beam staring microwave Doppler radar sensor. However, it should be appreciated that other object detecting sensors including other types of radar sensors, video imaging cameras, and laser sensors may be employed to detect the presence of an object, track the relative movement of the detected object, and determine the range measurements R₁and R₂, and range rate measurements {dot over (R)}₁and {dot over (R)}₂that are processed according to the present invention. The target object <b>16</b> is shown having an estimated crossing of the baseline B at a location C with a crossing location distance L from center point O. The crossing location distance L can also be expressed as the distance from the point O midway between sensors <b>12</b>A and <b>12</b>B (e.g., center of bumper) and crossing location C.

The collision detection system and method of the present invention advantageously estimates the crossing location C of the target object <b>16</b> as a function of range and range rate measurements, without the requirement of acquiring an azimuth angle measurement of the object <b>16</b>. Thus, the collision detection system of the present invention is able to use a reduced complexity and less costly sensing arrangement, while obtaining a crossing location C estimation. While a pair of sensors <b>12</b>A and <b>12</b>B are shown, it should be appreciated that any number of two or more sensors may be employed to estimate the crossing location C of one or more target objects.

In order to track object <b>16</b> in coverage zone <b>15</b>, the collision detection system may assume that the object <b>16</b> is a point reflector having a relative velocity vector S substantially parallel to the longitudinal axis of the vehicle <b>10</b>, which is the anticipated axis of travel of the vehicle <b>10</b>. The crossing location C is the signed lateral coordinate of the target object <b>16</b> where the object <b>16</b> is expected to cross the sensor baseline B (the line passing through the two sensors <b>12</b>A and <b>12</b>B along the y-axis). In the embodiment where the two sensors <b>12</b>A and <b>12</b>B are mounted on opposite sides of the front bumper of a host vehicle <b>10</b>, the side of the vehicle <b>10</b> to be affected by a potential collision can be determined based on the estimated crossing location C.

Based on the assumption that the target object <b>16</b> is assumed to have a relative velocity vector which is roughly parallel to the host vehicle <b>10</b> longitudinal axis, the following equation defines the crossing location

<maths id="MATH-US-00001" num="00001"><math overflow="scroll"><mrow><mi>C</mi><mo>=</mo><mfrac><mrow><msubsup><mi>R</mi><mn>1</mn><mn>2</mn></msubsup><mo>-</mo><msubsup><mi>R</mi><mn>2</mn><mn>2</mn></msubsup></mrow><mrow><mn>2</mn><mo>⁢</mo><mi>d</mi></mrow></mfrac></mrow></math></maths><img file="US7777618B2_D0001.tif" />

The crossing location C is determined as the distance midway between sensors <b>12</b>A and <b>12</b>B to the crossing point on baseline B. The crossing location C of the target object <b>16</b> is determined as described herein according to first and second embodiments of the present invention.

Referring to <figref idref="DRAWINGS">FIG. 3</figref>, the collision detection system <b>18</b> is shown including radar sensors <b>12</b>A and <b>12</b>B and a controller <b>20</b>. Controller <b>20</b> preferably includes a microprocessor-based controller having microprocessor <b>22</b> and memory <b>24</b>. Memory <b>24</b> may include random access memory (RAM), read-only memory (ROM), and electrically erasable programmable read-only memory (EEPROM). Controller <b>20</b> may be a commercially available off-the-shelf controller and may be dedicated to any one or more of target tracking, adaptive cruise control, and crash processing, according to some examples, or may share processing capability with other vehicle functions.

The controller <b>20</b> receives the range measurement R₁and range rate measurement {dot over (R)}₁from first radar sensor <b>12</b>A, and likewise receives the range measurement R₂and range rate measurement {dot over (R)}₂from the second radar sensor <b>12</b>B. Controller <b>20</b> processes the received range measurements R₁and R₂and range rate measurements {dot over (R)}₁and {dot over (R)}₂with a crossing location estimation routine according to the present invention. The controller <b>20</b> may further process the estimated crossing location estimation C to initiate countermeasures.

The controller <b>20</b> generates an output signal <b>26</b> in the event that an anticipated vehicle collision has been determined. The output signal <b>26</b> may be supplied as an input to one or more devices in the vehicle, such as an adaptive cruise control system <b>28</b>, seat belt pretensioner <b>30</b>, and one or more warning devices <b>32</b>. The adaptive cruise control system <b>28</b> may employ the estimated crossing location C of object <b>16</b> to control speed of the host vehicle <b>10</b>. The seat belt pretensioner may be controlled to pretension the seat belt just prior to an anticipated vehicle collision to eliminate slack in the restraining device, and may deploy only certain restraining devices based on the estimated crossing location C. The one or more warning devices <b>30</b> may be employed to warn the vehicle operator and occupants of an anticipated vehicle collision and the estimated location C of impact on the host vehicle <b>10</b>. It should be appreciated that other devices may be deployed responsive to signal <b>26</b> including vehicle air bags, pop-up roll bars, as well as other safety-related devices.

Referring to <figref idref="DRAWINGS">FIG. 4</figref>, a target crossing location estimator <b>34</b> is generally shown receiving the range measurements R₁and R₂and range rate measurements {dot over (R)}₁and {dot over (R)}₂, generated by first and second sensors <b>12</b>A and <b>12</b>B. The range and range rate measurements R₁and R₂and {dot over (R)}₁and {dot over (R)}₂are processed by the estimator <b>34</b>, which includes a programmed routine <b>40</b> estimating a crossing location C of the object relative to the baseline B of the sensors <b>12</b>A and <b>12</b>B. Further, the estimator <b>34</b> may estimate target speed S of the target object.

The crossing location estimation of the present invention assumes that the target object is moving straight and at a constant speed generally parallel to the longitudinal axis of the host vehicle <b>10</b>. The crossing location estimation assumes that the target object <b>16</b> is a point reflector having a velocity vector relative to the host vehicle <b>10</b> that is substantially parallel to the vehicle longitudinal axis.

Referring to <figref idref="DRAWINGS">FIG. 5</figref>, the W-plane is shown as a plane having data plotted on horizontal and vertical coordinates for data measured with one of sensors <b>12</b>A and <b>12</b>B. While data from one of sensors <b>12</b>A and <b>12</b>B is shown in <figref idref="DRAWINGS">FIG. 5</figref>, it should be appreciated that data from both sensors <b>12</b>A and <b>12</b>B is processed. The vertical coordinate represents the squared range R²values, while the horizontal coordinate represents the squared product of range and range rate (R·{dot over (R)})²values. The pairs of computed values for each of data measurements may be plotted in the W-plane as shown by points <b>64</b> for X number of measurements taken with each of sensors <b>12</b>A and <b>12</b>B. A least-squares fit line <b>66</b> is generated based on a close fit to the plurality of plotted measurements <b>64</b>.

While a least-squares fit line is shown and described herein in connection with the W-plane, it should be appreciated that other curves, both linear and non-linear, may be defined based on the pairs of data for N measurements <b>64</b>, without departing from the teachings of the present invention. Further, while a plot is shown in the W-plane, it should be appreciated that the controller <b>20</b> may process the data measured via first and second sensors <b>12</b>A and <b>12</b>B without providing a viewable plot, as the plot is merely illustrative of the processing of the data provided by a microprocessor-based controller <b>20</b>.

The speed S may be estimated from an interpretation of the fitted curve <b>66</b>.

<maths id="MATH-US-00002" num="00002"><math overflow="scroll"><mfrac><mn>1</mn><msup><mi>S</mi><mn>2</mn></msup></mfrac></math></maths><img file="US7777618B2_D0002.tif" /><br /> represents the slope of curve <b>66</b> as defined by horizontal segment <b>70</b> and vertical segment <b>72</b>. Accordingly, the speed S of the object relative to the host vehicle may be estimated based on the slope of curve <b>66</b>. While a straight line curve <b>66</b> is shown in <figref idref="DRAWINGS">FIG. 5</figref>, it should be appreciated that some higher-order curve may be employed to define the relationship of the sample points.

The collision detection system of the present invention advantageously estimates the crossing location C of the target object <b>16</b>, which is the location at which the object is estimated to cross the baseline B of the first and second sensors <b>12</b>A and <b>12</b>B. According to one embodiment, the crossing location C is determined from a point O midway between the two sensors <b>12</b>A and <b>12</b>B. By estimating the crossing location C of the object <b>16</b>, the controller <b>20</b> is able to estimate where the target object <b>16</b> may impact the host vehicle <b>10</b>. This enables the controller <b>20</b> to take pre-emptive action such as to avoid the accident and/or initiate certain devices in anticipation of a collision at the estimated crossing location C. The estimated crossing location C of the object <b>16</b> is estimated according to a first embodiment shown in <figref idref="DRAWINGS">FIGS. 6 and 7</figref>, and according to a second embodiment shown in <figref idref="DRAWINGS">FIGS. 8 and 9</figref>.

Referring to <figref idref="DRAWINGS">FIG. 6</figref>, a routine <b>80</b> for estimating the crossing location C of a target object is shown according to the first embodiment of the present invention. Routine <b>80</b> employs the data plotted in the W-plane for both of sensors <b>12</b>A and <b>12</b>B. One example of data plotted in the W-plane for both of sensors <b>12</b>A and <b>12</b>B is shown in <figref idref="DRAWINGS">FIG. 7</figref>. As seen in <figref idref="DRAWINGS">FIG. 7</figref>, a least-squares line <b>66</b>A is drawn through the data representing measurements taken with the first sensor <b>12</b>A. Likewise, a least-squares line <b>66</b>B is determined with respect to the data representing measurements taken with the second sensor <b>12</b>B.

Routine <b>80</b> begins at step <b>82</b> and proceeds to get the current range measurement R₁and R₂and range rate measurements {dot over (R)}₁and {dot over (R)}₂sensed by first and second radar sensors in step <b>84</b>. Routine <b>80</b> may associate data with the particular target object by way of an object tracker. The object tracker tracks each object based on the combination of range and range rate measurements taken with each of first and second sensors <b>12</b>A and <b>12</b>B. If the current range and range rate measurements are sufficiently close in value to the predicted range and range rate values, the object measurement data is assumed to pertain to the same object. The tracking of each detected object with each sensor allows for a consistent stream of measurement data at incremental time periods k, k+1, k+2, etc. for each sensed object.

In step <b>86</b>, the W-plane quantities corresponding to measurements for each of the first and second sensors are calculated which include the W-plane quantities of R²and (R·{dot over (R)})²in step <b>86</b>. In step <b>88</b>, routine <b>80</b> selects the N most recent W-plane points from data measured with each of the two sensors <b>12</b>A and <b>12</b>B. The squared range and squared product of range and rate values, R²and (R·{dot over (R)})², respectively, for each of N measurements taken by each of first and second sensors <b>12</b>A and <b>12</b>B are preferably stored in memory and are processed by controller <b>20</b> as explained herein. It should be appreciated that the number (N) of measurements may include thirty, according to one example, or may include fewer or greater number of measurements for each of the sensors <b>12</b>A and <b>12</b>B. The processing of a greater number of measurements may result in less noise, but may be less responsive to maneuvers between the object and the host vehicle. Accordingly, the number (N) of measurements from each of first and second sensors <b>12</b>A and <b>12</b>B that are processed is a compromise and may vary depending on the application.

Routine <b>80</b> may include optional step <b>90</b> of discarding one or more outlier data points from each of the two sensors. The outlier removal enhancement may remove one or more data points from each window, after identifying them as being in substantial disagreement with the other data points of the window. This is done before calculating the least-squares line for each window.

Proceeding to step <b>92</b>, routine <b>80</b> calculates a least-squares line for each sensor using the remaining data points in each window. That is, the data measured with sensor <b>12</b>A is used to calculate a first least-squares line <b>66</b>A, while the data measured with sensor <b>12</b>B is used to calculate a second least-squares line <b>66</b>B. The least-squares lines <b>66</b>A and <b>66</b>B corresponding to the first and second sensors <b>12</b>A and <b>12</b>B, respectively, which are shown in one example in <figref idref="DRAWINGS">FIG. 7</figref>, may be adjusted to constrain the slope of the lines <b>66</b>A and <b>66</b>B to be equal to one another. By constraining the two least-squares line <b>66</b>A and <b>66</b>B to have the same slope, enhanced accuracy of the crossing location estimation can be achieved. The slope of the W-plane trace is the inverse of the target's relative speed squared. Because of this relationship, if the data from two sensors tracking the same point target are plotted in the W-plane, the resulting traces should be parallel.

Next, in step <b>94</b>, routine <b>80</b> calculates the W-plane vertical distance V which is the vertical distance between the two lines <b>66</b>A and <b>66</b>B in the neighborhood (window) of the two sets of points for the corresponding two sensors. The vertical distance V is preferably taken near the center of the windowed lines <b>66</b>A and <b>66</b>B. In step <b>96</b>, routine <b>80</b> divides the vertical separation V by twice the separation distance 2d of sensors <b>12</b>A and <b>12</b>B to obtain the crossing location C. According to the embodiment shown, the crossing location C is determined relative to the point O midway between the two sensors <b>12</b>A and <b>12</b>B.

According to one example, if line <b>66</b>B corresponding to sensor <b>12</b>B is below lines <b>66</b>A corresponding to sensor <b>12</b>A, then the crossing location C of the target object <b>16</b> is negative, that is, it is on the driver side of the vehicle, according to one arrangement. Thus, if line <b>66</b>A corresponding to sensor <b>12</b>A is below line <b>66</b>B corresponding to sensor <b>12</b>B, then the crossing location C of the target object <b>16</b> is positive, that is, it is on the passenger side of the vehicle, as compared to the driver side. By knowing which side of the vehicle the object is expected to collide with, enhanced countermeasures can be initiated.

The first embodiment employing the vertical separation technique in the W-plane may be generally less sensitive to maneuvers and accelerations. In this approach, only the vertical separation is required to estimate the crossing location, and since the two ideal measurement curves <b>66</b>A and <b>66</b>B are similarly shaped, any ill effects of the fitted lines approximately cancel out. Additionally, the W-plane approach is generally insensitive to any distributed nature of the target.

Referring to <figref idref="DRAWINGS">FIGS. 8 and 9</figref>, a time-domain approach to estimating the crossing location C of a target object <b>16</b> is shown according to the second embodiment of the present invention. The time-domain approach to estimating the crossing location employs an estimator <b>34</b>′ having tracking filters <b>100</b> and <b>102</b> coupled to corresponding radar sensors <b>12</b>A and <b>12</b>B to produce a range R estimate for each sensor. The tracking filters <b>100</b> and <b>102</b> may also receive range rate {dot over (R)}; however, the tracking filters <b>100</b> and <b>102</b> may operate without range rate. The estimator <b>34</b>′ further includes mathematical square functions <b>104</b> and <b>106</b> for calculating the mathematical square of the outputs of tracking filters <b>100</b> and <b>102</b>, respectively. A subtractor <b>108</b> computes the difference between the outputs of square functions <b>104</b> and <b>106</b>. Additionally, estimator <b>34</b>′ employs a divider <b>110</b> for dividing the computed difference by twice the separation distance (2d) of sensors <b>12</b>A and <b>12</b>B. The output of divider <b>110</b> is applied to a low pass filter <b>112</b> to provide the crossing location estimate C in block <b>114</b>.

Referring to <figref idref="DRAWINGS">FIG. 9</figref>, a routine <b>120</b> is shown for estimating the crossing location C of a target object employing estimator <b>34</b>′ according to the second embodiment. Routine <b>120</b> begins at step <b>122</b> and proceeds to step <b>124</b> to get the range measurements R₁and R₂from both radar sensors <b>12</b>A and <b>12</b>B. Optionally, range rate {dot over (R)}₁and {dot over (R)}₂measurements may also be obtained. Proceeding to step <b>126</b>, routine <b>120</b> processes each set of radar sensor measurements from sensors <b>12</b>A and <b>12</b>B using the range tracking filters <b>100</b> and <b>102</b>, respectively. The filters <b>100</b> and <b>102</b> may optionally also use the range rate measurements {dot over (R)}₁and {dot over (R)}₂which may offer enhanced estimation of the crossing location.

Next, routine <b>120</b> proceeds to step <b>128</b> to find the difference of the squares of the two current range estimates from the tracking filters. This is performed by the subtractor <b>108</b>. Next, in step <b>130</b>, routine <b>120</b> divides the difference by twice the sensor separation distance 2d. In step <b>132</b>, the divided difference is low pass filtered to get the estimated crossing location C. Routine <b>120</b> is then completed in step <b>134</b>.

The time-approach estimation <b>34</b>′ advantageously does not require range rate measurements from sensors <b>12</b>A and <b>12</b>B to obtain an estimation of the crossing location C. If sufficient range rate information is available from sensors <b>12</b>A and <b>12</b>B, such range rate information may advantageously enhance the tracking filter processing.

Accordingly, the collision detection system of the present invention advantageously estimates the crossing location C in a simplified and cost affordable system. The present collision detection system quickly estimates the crossing location C much faster than prior known approaches. Additionally, the collision detection system of the present invention handles maneuvers and accelerations better than prior known single-sensor approaches. By quickly and accurately determining the crossing location C of an object with respect to the host vehicle <b>10</b>, the system is able to quickly initiate countermeasures which may occur based on the estimated location of a potential collision.

It will be understood by those who practice the invention and those skilled in the art, that various modifications and improvements may be made to the invention without departing from the spirit of the disclosed concept. The scope of protection afforded is to be determined by the claims and by the breadth of interpretation allowed by law.